Definition:
U-shaped development, also known as U-shaped learning, is the typical pattern by which select physical, artistic, and cognitive skills are developed. It is called “U” shape development because of the shape of the letter U in correlation to a graph, skills developed in the “U shaped” fashion begin on a high position on a graph’s Y-axis. The skills start out at a high performance level and over time the skills descend to a lower position on the Y-axis. After another period of time the skill once again ascends to a higher position on the y-axis. A “U” shaped time line is created of the skills development.
Further Reading:
Book: The Principles of Product Development Flow by Donald G. Reinertsen